Alkylation process for increased conversion and reduced catalyst use

ABSTRACT

The invention relates to a process for the production of alkylated aromatic compounds comprising introducing olefin and aromatic compounds into at least first and second vertically spaced catalytic reaction zones in an alkylation unit under alkylation reaction conditions to provide an alkylated product, wherein the second catalytic reaction zone is positioned above the first catalytic reaction zone; wherein aromatic compound from each of the at least first and second catalytic reaction zones are contacted with a cooling means for re-condensing at least a portion of the aromatic compounds vaporized from the exothermic heat of reaction of the alkylation process; and wherein the olefin is introduced into the at least first and second catalytic reaction zones via respective first and second olefin feed streams at respective olefin feed rates such as to maintain olefin partial pressures at inlets to at least first and second catalytic reaction zones which vary by less than about ten percent. The invention additionally relates to an apparatus for practicing the alkylation process of the invention.

CROSS-REFERENCE TO RELATED APPLICATION

This application, pursuant to 35 U.S.C. §120, claims benefit to U.S.patent application Ser. No. 11/489,017 filed Jul. 19, 2006, now U.S.Pat. No. 7,632,974. That application is incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improved catalytic distillationprocess for the production of alkylated aromatics from the alkylationreaction of olefin and aromatic compounds.

2. Description of the Related Art

The advantages of the catalytic distillation process over conventionalliquid phase alkylation processes are well recognized. See, for example,U.S. Pat. Nos. 4,307,254, 4,443,559, 4,849,569, to Smith, Jr., U.S. Pat.No. 5,243,115 to Smith, Jr. et al., and U.S. Pat. No. 4,439,350 toJones, Jr. et al.

Some of the most common alkylation reactions include the alkylation ofbenzene with either ethylene or propylene to produce ethylbenzene orcumene, respectively. Ethylbenzene is particularly important for its usein the production of styrene, a precursor to polystyrene, while cumeneis particularly important for its use in the production of phenol andacetone.

The catalytic distillation units thus far used are not, by themselves,capable of the complete conversion of the olefin and aromatic reactantsto alkylated aromatic products. Accordingly, the catalytic distillationprocess typically includes an alkylation finishing reactor, operated inthe liquid phase, for converting any remaining unreacted olefin andaromatic compounds to alkylated aromatic products with nearly completeconversion of the olefin. See published U.S. application Ser. No.2004/0254412 to Pohl.

While the catalytic distillation method for alkylation reactions hasprovided many benefits, there remain several areas in need ofimprovement. For example, the process is known to suffer from a lack ofreaction efficiency (i.e., impeded olefin conversion). This impedance ofolefin conversion is primarily caused by an inability to control therequired olefin partial pressure in the alkylation unit.

In particular, the heat of reaction (the reaction occurring in theliquid phase over the catalyst) causes partial vaporization of aromaticcompounds, and a significant increase in the vapor rate from thelowermost portion of the catalyst to the uppermost portion. Gaseousolefin, flowing counter-currently upwards through the reactor, isabsorbed into the liquid phase and is consumed by reaction over thecatalyst. Since vapor-liquid equilibrium is approximately maintained,the result is a continuous reduction in olefin partial pressure and acorresponding decrease in liquid phase olefin concentration from thelowermost portion of the catalyst to the uppermost portion. Thisreduction in liquid phase olefin concentration causes correspondinglylower reaction rates and requires an ever-greater amount of catalyst tomaintain the same incremental olefin conversion as it proceeds up thereactor.

Since the cost of the catalyst is typically significant, larger amountsof catalyst can result in a significant capital investment for theprocess. In addition, a larger amount of catalyst further exacerbatesthe capital and operational costs of the process by requiring a largeralkylation reactor for housing the catalyst.

Some degree of control of olefin partial pressures have been achieved inthe art, but these have not resulted in maintaining satisfactory olefinconversion rates in all catalyst beds. For example, improved olefinconversion rates have been achieved throughout the catalyticdistillation unit by employing an optimal benzene vapor feed rate to thebottom of the catalytic distillation unit in combination withcontrolling the number of olefin injection points and the flow rate toeach injection point. However, even with this improvement, olefinconversion rates still drop off sharply in the middle to upper catalystbeds.

There is a need, therefore, for an improved catalytic distillationprocess for alkylation reactions with an improved conversion rate of theolefin. There is a particular need for improving the conversion rate ofthe olefin by better maintaining a desired olefin partial pressurethroughout the catalyst of the catalytic distillation unit. Such animprovement would allow for the use of lesser amounts of catalyst, andconsequently, a reduction in size of the alkylation reactor, and/orgreater overall olefin conversion across the alkylation reactor.

SUMMARY OF THE INVENTION

These and other objectives have been achieved, firstly, by providing aprocess for the production of alkyl aromatic compounds in a catalyticdistillation reactor, wherein variations in vapor loading and olefinpartial pressures in the catalytic distillation reactor are reduced andthe effective number of reaction stages can be increased. The processcomprises the steps of:

introducing olefin and aromatic compounds into at least first and secondvertically spaced catalytic reaction zones in an alkylation unit underalkylation reaction conditions to provide an alkylated product, whereinsaid second catalytic reaction zone is positioned above the firstcatalytic reaction zone;

wherein vaporous aromatic compounds from each of the at least first andsecond catalytic reaction zones are contacted with a cooling means forcondensing at least a portion of said vaporous aromatic compounds;

and wherein the olefin is introduced into the at least first and secondcatalytic reaction zones via respective first and second olefin feedstreams at respective olefin feed rates such as to maintain olefinpartial pressures at inlets to at least first and second catalyticreaction zones which vary by less than about ten percent.

In a specific embodiment, the process comprises:

a) introducing one or more aromatic compounds and one or more olefinsinto a catalytic distillation unit having at least two lower beds, alowermost bed, and an uppermost bed of a first alkylation catalyst, thecatalytic distillation unit operated in a combination liquid phase-vaporphase mode under alkylation reaction conditions to produce a liquidalkylator bottoms effluent comprising alkylated aromatic compounds andunreacted aromatic compound discharging below the lowermost bed, and analkylator vapor overhead stream comprising unreacted aromatic compoundand unreacted olefin discharging above the uppermost bed;

b) condensing the alkylator vapor overhead stream to form a condensedalkylator overhead stream and directing said condensed alkylatoroverhead stream into a finishing reactor having a second alkylationcatalyst and operated in a liquid phase under alkylation reactionconditions wherein the unreacted aromatic compound and unreacted olefinin the alkylator overhead stream are converted to alkylated aromaticcompounds with substantially complete consumption of the unreactedolefin, thereby producing a finishing reactor effluent comprisingalkylated aromatic compound and essentially no unreacted olefin;

c) removing a substantial portion of any volatile compounds in thefinishing reactor effluent to form a stripped finishing reactoreffluent;

d) cooling at least a portion of the finishing reactor effluent to atemperature sufficiently low for condensing at least a portion ofvaporous aromatic compounds in the catalytic distillation unit, therebyforming a stripped and cooled finishing reactor effluent; and

e) directing said stripped and cooled finishing reactor effluent aboveat least the two lower beds of the first alkylation catalyst duringoperation of the catalytic distillation unit.

In another embodiment, the process comprises:

a) introducing one or more aromatic compounds and one or more olefinsinto a catalytic distillation unit having at least two lower beds, alowermost bed, and an uppermost bed of a first alkylation catalyst, thecatalytic distillation unit operated in a combination liquid phase-vaporphase mode under alkylation reaction conditions to produce a liquidalkylator bottoms effluent comprising alkylated aromatic compounds andunreacted aromatic compound discharging below the lowermost bed and analkylator vapor overhead stream comprising unreacted aromatic compoundand unreacted olefin discharging above the uppermost bed;

b) substantially removing any alkylated aromatic compounds in thealkylator vapor overhead stream by use of a suitable absorbent capableof selectively removing alkylated aromatic compounds in the presence ofunreacted aromatic compound and unreacted olefin, thereby producing ascrubbed alkylator overhead stream;

c) condensing the scrubbed alkylator overhead stream to form a condensedand scrubbed alkylator overhead stream and directing said condensed andscrubbed alkylator overhead stream into a finishing reactor having asecond alkylation catalyst and operated in a liquid phase underalkylation reaction conditions wherein the unreacted aromatic compoundand unreacted olefin in the scrubbed alkylator overhead stream areconverted to alkylated aromatic compounds with substantially completeconsumption of the unreacted olefin, thereby producing a finishingreactor effluent comprising alkylated aromatic compound and essentiallyno unreacted olefin;

d) removing a substantial portion of any volatile compounds in thefinishing reactor effluent to form a stripped finishing reactoreffluent;

e) cooling at least a portion of the stripped finishing reactor effluentto a temperature sufficiently low for condensing at least a portion ofvaporous aromatic compounds in the catalytic distillation unit, therebyforming a stripped and cooled finishing reactor effluent, and

f) directing said stripped and cooled finishing reactor effluent aboveat least the two lower beds of the first alkylation catalyst duringoperation of the catalytic distillation unit.

In another embodiment, the process comprises:

a) introducing one or more aromatic compounds and one or more olefinsinto a catalytic distillation unit having a first alkylation catalystcomprising a vertical arrangement of three to ten baled catalyst unitsand having a lowermost baled catalyst unit and an uppermost baledcatalyst unit, the catalytic distillation unit operated in a combinationliquid phase-vapor phase mode under alkylation reaction conditions toproduce a liquid alkylator bottoms effluent comprising alkylatedaromatic compounds and unreacted aromatic compound discharging below thelowermost baled catalyst unit and an alkylator vapor overhead streamcomprising unreacted aromatic compound and unreacted olefin dischargingabove the uppermost baled catalyst unit, wherein olefin is fed to thefirst alkylation catalyst by two to seven split olefin feed linesfeeding an equal number of baled catalyst units of a lower portion ofsaid vertical arrangement of three to ten baled catalyst units, whereinthe number of baled catalyst units is greater than the number of splitolefin feed lines, thereby leaving an upper portion of baled catalystunits without olefin feed lines;

b) substantially removing any alkylated aromatic compounds in thealkylator overhead stream by use of a suitable absorbent capable ofselectively removing alkylated aromatic compounds in the presence ofunreacted aromatic compound and unreacted olefin, thereby producing ascrubbed alkylator overhead stream;

c) condensing the scrubbed alkylator overhead stream to form a condensedand scrubbed alkylator overhead stream and directing said condensed andscrubbed alkylator overhead stream into a finishing reactor having asecond alkylation catalyst and operated in a liquid phase underalkylation reaction conditions wherein the unreacted aromatic compoundand unreacted olefin in the scrubbed alkylator overhead stream areconverted to alkylated aromatic compounds with substantially completeconsumption of the unreacted olefin, thereby producing a finishingreactor effluent comprising alkylated aromatic compound and essentiallyno unreacted olefin;

d) removing a substantial portion of any volatile compounds in thefinishing reactor effluent to form a stripped finishing reactoreffluent;

e) cooling at least a portion of the stripped finishing reactor effluentto a temperature sufficiently low for condensing at least a portion ofvaporous aromatic compounds in the catalytic distillation unit, therebyforming a stripped and cooled finishing reactor effluent, and

f) directing said stripped and cooled finishing reactor effluent to thefirst alkylation catalyst during operation of the catalytic distillationunit, wherein cooled finishing reactor effluent is split into a numberof split feed lines equal to or greater than the number of olefin splitlines, each of the split feed lines of cooled finishing reactor effluentinjecting above each of the lower portion of baled catalyst units beingfed by olefin.

The invention additionally includes a catalytic distillation apparatusfor achieving the process described above. In a preferred embodiment,the catalytic distillation system comprises:

a) a catalytic distillation unit having a first alkylation catalyst, analkylator bottoms outlet below a lowermost portion of the firstalkylation catalyst for discharging a liquid alkylator bottoms effluent,and an alkylator overhead outlet above an uppermost portion of the firstalkylation catalyst for discharging an alkylator vapor overhead stream,wherein said catalytic distillation unit is operable in a combinationliquid-vapor phase under alkylation reaction and distillationconditions;

b) means for selectively and substantially removing any alkylatedaromatic compounds in the alkylator vapor overhead stream to produce ascrubbed alkylator overhead stream;

c) means for condensing and transferring said scrubbed alkylatoroverhead stream to a finishing reactor having a second alkylationcatalyst and a finishing reactor outlet for discharging reactedfinishing reactor effluent, wherein said finishing reactor is operablein a liquid phase under alkylation conditions;

d) means for cooling said finishing reactor effluent to a temperaturesufficiently low for condensing at least a portion of vaporous aromaticcompounds in the catalytic distillation unit; and

e) means for directing cooled finishing reactor effluent into the firstalkylation catalyst.

The invention advantageously controls olefin partial pressure byre-condensing the aromatics, mostly aromatic reactant (e.g., benzene)and to a lesser extent alkylated aromatics (e.g., diethylbenzene,triethylbenzene, etc.) vaporized from the exothermic heat of reaction.By re-condensing the aromatics, the flow of aromatic vapor no longersubstantially increases up the alkylation column, and this in turnallows for more uniform, optimal/beneficial distribution of olefinpartial pressure feed to each the catalyst beds and a more uniformcounter-current vapor-liquid flow regime. Accordingly, in contrast towhat has been practiced in the prior art, the olefin feed rates at eachinjection point are no longer required to increase up the column inorder to maximize olefin partial pressure and reaction rate.

Furthermore, since the flow of aromatic vapor no longer substantiallyincreases up the alkylator column, the initial aromatic vapor feed atthe bottom of the alkylator can be significantly higher than in a priorart while maintaining or reducing the vapor loading at the top of thealkylator. A reduction in vapor loading at the top of the alkylatorallows for a smaller diameter alkylator, since the hydraulic loading atthe top of the alkylator is controlling.

Furthermore, a higher initial flow of aromatic vapor at the bottom ofthe alkylator allows for a higher initial flow of olefin at the bottombed of the alkylator, while not exceeding any design olefin partialpressure constraints. For example, four olefin feed injectionsdistributed, from bottom, as 18%/21%/24%/37% in a prior art process cannow be four olefin injections distributed as 33%/26%/22%/19%.

The higher olefin flow to each of the lower catalyst beds (includingfresh make-up olefin feed plus unreacted olefin that exits the previousbed) and resulting higher olefin conversion in each of these bedssignificantly increases the catalyst productivity (olefin converted pervolume of catalyst) in the lower catalyst beds. This is in contrast tothe lower but ever increasing flow of olefins and lower olefinconversion of the prior art.

Moreover, a reduction in alkylator diameter with the same catalyst bedheight results in even higher catalyst productivity in the lowercatalyst beds since olefin conversion increases and catalyst volumedecreases. The resulting higher catalyst productivity has no negativeconsequences because catalyst productivity in both cases is sufficientlylow so as not to be a significant factor in catalyst run-length or lifeexpectancy.

The amount of olefin converted across the lower beds (i.e., those bedsthat receive fresh make-up olefin feed) is now significantly higher thanthe prior art. For example, the olefin converted across the lower fourcatalyst beds in a prior art process is typically 70% of the totalolefin feed. This is in contrast to the present invention wherein olefinconversion is typically at least 72% of the total olefin feed, but with40% less catalyst.

The upper catalyst beds (i.e., those beds that do not receive freshmake-up olefin feed) also perform better. These catalyst beds furtherreact un-converted olefin exiting the lower beds so that the overall CDalkylator olefin conversion is at least 75-80% (when a finishing reactoris employed), and provide an allowance for run-length (catalyst ageing).First, the partial pressure of olefin is higher, even without theinjection of fresh make-up olefin feed, because of the condensation ofvaporized aromatics, compared with the prior art process. Second, thereis now less unconverted olefin from the lower catalyst beds entering theupper catalyst beds compared with the prior art process. Third, for thesame amount of total catalyst and smaller diameter alkylator, there isless catalyst contained in the lower beds, and thus more catalystcontained in the upper beds, compared with the prior art process. Thismeans there are now a greater number of upper catalyst beds of the samebed height, and thus a greater total upper bed height available tocontact and convert the olefin.

The improved lower catalyst bed operation and improved upper catalystbed operation results in significantly higher olefin conversion in thealkylator with the same amount of catalyst compared with the prior artprocess (5% to 15% higher alkylator conversion, depending on the designrun-length); or significantly less catalyst (30% to 40% less catalyst,depending on run-length catalyst allowance) required to achieve the sameolefin conversion as compared with the prior art process.

The higher olefin conversion of the present invention allows for asmaller finishing reactor and less finishing reactor catalyst than theprior art since less olefin needs to be converted in the finishingreactor. If the olefin conversion of the present invention isapproximately the same as compared with prior art processes, this wouldstill allow for a smaller alkylator and less alkylator catalyst. Eithercase provides economic benefits.

Furthermore, since there can be more total catalyst beds in a smallerdiameter alkylator having the same amount of total catalyst, in contrastto what has been practiced in the prior art, there can now be moreinjection points to distribute the olefin feed amongst additionalcatalyst bed. For example, four olefin feed injections distributed (frombottom) as 18%/21%/24%/37% in a prior art process can now be five olefininjections distributed as 28%/23%/19%/16%/14%.

The more uniform distribution of olefin to more catalyst beds means: 1)more beds receive fresh make-up olefin feed and operate at highproductivity; and 2) there are more beds operating at maximum olefinpartial pressure. This effectively increases the number of reactionstages. The greater distribution of olefin feed and lower catalyst bedproductivity can also result in more uniform catalyst aging andpotentially longer catalyst run length.

More CD alkylator beds at maximum olefin partial pressure results instill higher conversion rates and lower required finishing reactorconversion. Overall, the average olefin partial pressure throughout thecatalytic distillation unit is higher in the present invention, andtherefore, the average reaction rate throughout the catalyticdistillation unit is higher.

In a particularly preferred embodiment, the invention provides the aboveadvantages by including a process for cooling the effluent from afinishing reactor and feeding the cooled finishing reactor effluent tothe alkylation catalyst during an alkylation reaction. The cooledfinishing reactor effluent advantageously helps maintain a desiredolefin partial pressure in the alkylation catalyst by effecting areduction in the vapor pressure of the aromatic by condensation of thearomatic. The process allows for an improved conversion of olefin (e.g.,90% instead of 80%) and/or a reduction in the amount of requiredcatalyst and a reduction in the size of the alkylation and/or finishingreactor. These improvements also allow for a reduction in costs andbetter product yields for the process.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are described herein with reference to the drawingswherein:

FIG. 1 is a view of a preferred catalytic distillation process of theinvention; and,

FIG. 2 is a view of a preferred distillation system coupled to element106 carrying the alkylator bottoms streamline.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As used herein, the term “aromatic” includes non-alkyl group-containingaromatic compounds, such as benzene and naphthalene, as well asalkyl-containing aromatic compounds, such as toluene, xylene, and thelike. The term “alkylated aromatic” refers to compounds to which one ormore additional alkyl groups are attached by the aromatic alkylationprocess described below.

Referring to FIG. 1, the process of the invention requires an alkylationunit corresponding to element 100, as shown. In the alkylation unit, oneor more olefin compounds and one or more aromatic compounds areintroduced into at least two (i.e., first and second) vertically spacedcatalytic reaction zones under alkylation reaction conditions, whereinthe second catalytic reaction zone is positioned above the firstcatalytic reaction zone. During operation of the alkylation unit, theolefin and aromatic compounds react on contact with the catalyst in eachof the reaction zones to produce one or more alkylated aromaticcompounds.

The alkylation unit 100 is typically a catalytic distillation unit thatoperates in a combination liquid phase-vapor phase mode and undersuitable alkylation reaction conditions, as known in the art.Preferably, the catalytic distillation unit 100 is operated at apressure of from about 270 psig to about 550 psig and a temperature offrom about 365° F. to about 482° F. (185° C. to about 250° C.), with anaromatics to olefin weight ratio in the preferred range of about 2.0 toabout 3.5. A prior known catalytic distillation unit has been previouslydescribed in detail in U.S. Pat. No. 4,849,569 to Smith, Jr.

The alkylation catalyst can be any suitable alkylation catalyst known inthe art. The preferred compositions and forms of such alkylationcatalysts have been previously described in detail in U.S. Pat. Nos.4,849,569 and 4,443,559 to Smith, Jr., both of which are incorporatedherein by reference in their entirety. A suitable alkylation catalyst,besides having the ability to catalyze an alkylation reaction, shouldhave an appropriate surface area and allow vapor to flow through it, asdescribed in U.S. Pat. No. 5,243,115 to Smith Jr., et al., and U.S. Pat.Nos. 4,215,011 and 4,302,356 to Smith Jr., all of which are incorporatedby reference herein in their entirety.

The alkylation catalyst is preferably a suitable acidic catalyst.Suitable acidic catalysts include molecular sieves (mole sieves) andcation exchange resins, as described in the patent references citedabove. Some particularly preferred catalysts include zeolite X, zeoliteY, zeolite L, TMA Offretite, mordenite, amorphous silica-alumina,zeolite BEA (beta), zeolite MWW, MFI catalyst, and zeolite BEA.

Preferably, the alkylation catalyst is in the form of discrete catalystbeds. In a preferred embodiment, the catalyst beds are in the form ofpackaged (i.e., baled) catalyst units vertically arranged in thecatalytic distillation unit. More preferably, an appropriate spacing isprovided between each of the vertically arranged baled catalyst units.For example, in a particularly preferred embodiment, the alkylationcatalyst contains a plurality of vertically arranged baled catalystunits wherein each baled catalyst unit is limited to approximately sixfeet in height with a spacing of 18 to 30 inches.

In a particular embodiment, the alkylation catalyst comprises at leasttwo, more preferably three, and more preferably four baled catalystunits in a vertical arrangement. In another embodiment, the alkylationcatalyst comprises five to ten baled catalyst units in a verticalarrangement. For example, the alkylation catalyst can comprise avertical arrangement of five, more preferably six, and even morepreferably, as shown in FIG. 1 (i.e., elements 103 a-103 g), seven baledcatalyst units having some spacing between each baled catalyst unit.

The process described above preferably further comprises a finishingreactor 119. The finishing reactor reacts unreacted aromatic compoundand unreacted olefin compound from the alkylator overhead stream toalkylated aromatic compounds in a highly efficient liquid phase processwhich allows for the substantially complete consumption of unreactedolefin. Accordingly, essentially no unreacted olefin remains after thefinishing process.

Since the finishing reactor operates more efficiently than alkylation inthe mixed vapor-liquid phases of the catalytic distillation unit, thefinishing reactor typically requires less catalyst than the catalyticdistillation unit. Finishing reactor 119 preferably operates at atemperature of from about 392° F. to about 446° F. (200° C. to about230° C.), a pressure of from about 550 psig to about 900 psig, and anaromatics to olefin mole ratio of from about 2.0 to about 10.0.

The alkylation catalyst of the finishing reactor can be the same ordifferent (compositionally and/or in physical design) than thealkylation catalyst of the alkylation unit. In order to distinguish thetwo alkylation catalysts where a finishing reactor is used, thealkylation catalyst of the alkylation unit will hereinafter be referredto as the “first alkylation catalyst” and the alkylation catalyst of thefinishing reactor as the “second alkylation catalyst.”

Whereas the the first alkylation catalyst is preferably in the form ofpackaged bales, the second alkylation catalyst is preferably in the formof a fixed bed of loose catalyst having any of the suitable compositionsfor alkylation catalysts as described above for the first alkylationcatalyst. The composition of the second alkylation catalyst is morepreferably selected from zeolite Y, zeolite BEA (beta), zeolite MWW,Mordenite, or MFI catalyst.

According to the invention, vaporous aromatic compounds from each of theat least first and second catalytic reaction zones is contacted withcooling means for condensing at least a portion of the vaporous aromaticcompounds. Any means known in the art for cooling can be used for thecooling means. For example, the cooling means can be a cooling elementto indirectly remove heat from the catalytic distillation unit to acolder process stream or utility.

Some examples of cooling elements include any of the suitable coolers orheat exchangers known in the art. Some more specific examples of coolingelements include pump-around coolers and bayonette-type U-tube heatexchangers (e.g., with the coolant on the tube side) inserted betweenthe catalyst beds and external shell-and-tube heat exchangers where thealkylator inter-bed mixture is forced to circulate through the tube sideof the heat exchanger (e.g., with the coolant on the shell side).

The cooling means can also be a cooled aromatic-containing stream whichis preferably at a temperature sufficiently low for the condensation,more preferably re-condensation, of at least a portion, more preferablya major portion, of the vaporized aromatic compounds. For example, acooled aromatics stream from feed source F-3 could be used forcondensing vaporous aromatics in the catalytic distillation unit, eitherin place of or in addition to the cooled finishing reactor effluent.

More preferably, the cooling means is cooled effluent from a finishingreactor. For example, in a preferred embodiment, cooling is accomplishedby first stripping the finishing reactor effluent of volatile compounds(e.g., in a lights stripper 102) before cooling the finishing reactoreffluent, and then directing the stripped and cooled finishing reactoreffluent above at least two lower catalyst beds.

The cooled finishing reactor effluent advantageously helps maintain adesired olefin partial pressure in the alkylation catalyst by effectinga reduction in the vapor pressure of the aromatic by re-condensation ofat least a major portion (e.g., equal to or greater than 90%) of thearomatics vaporized from the exothermic heat of reaction. Theimprovement allows for an improved conversion rate of the olefin in theprocess, which allows for, inter alia, a reduction in the amount ofrequired catalyst and a reduction in the size of the alkylation reactor.These improvements allow for a reduction in costs and better productyields for the process.

The first alkylation catalyst is preferably located in the vicinity ofthe lower portion of the catalytic distillation unit 100. Morepreferably, a sufficient space is provided below the lowermost portionof the first alkylation catalyst for the introduction and accumulationof aromatic and/or olefinic vapors or liquids. Similarly, it ispreferred that the catalytic distillation unit 100 include a sufficientspace above the uppermost portion of the first alkylation catalyst forinclusion of an absorbent (e.g., 101) and/or a lights stripper (e.g.,102), each of which are described in further detail below. A space belowthe lowermost and/or above the uppermost portions of the firstalkylation catalyst can range from, for example, one-twentieth toone-half the height of the alkylation unit. This range is given forpurposes of illustration and is not to be construed as a limitation ofthe scope of the invention. Values outside of this range can be usedwhere appropriate.

An olefin feed F-1 and an aromatics feed F-2 are introduced into atleast first and second catalytic reaction zones of an alkylation unit bysuitable olefin and aromatics feed lines (i.e., olefin-containing andaromatic-containing streams). Each feed line can be independently splitor unsplit and connected to the alkylation unit directly or indirectlyto bring the olefin or aromatics feed in contact with (i.e., into) thealkylation catalyst. The olefin feed and aromatics feed can beintroduced into the alkylation unit separately in the form of separateolefin and aromatic feed lines, or alternatively, as a combinedolefin-aromatics mixture in one or more feed lines.

In one embodiment, olefin is fed to the first alkylation catalyst at twoor more locations of the catalyst by use of two or more streams ofolefin. For example, the olefin feed line can be split into two to ten,or four to eight split olefin feed lines, either of which feed into avertical arrangement of two to ten or four to eight baled catalyst unitsof the first alkylation catalyst, respectively. Preferably, each olefinfeed line directs olefin to (and more preferably below) a single baledcatalyst unit. The number of split olefin feed lines and number of baledcatalyst units are independent of each other provided that there are atleast as many baled catalyst units as there are olefin feed lines.

For example, in a preferred embodiment, as shown in FIG. 1, olefin feedF-1 is sent to the first alkylation catalyst via an olefin feed line104, which is split into four streams 104 a-104 d, each of which feedsolefin to each of four baled catalyst units (i.e., 103 a-d) of a totalof seven vertically arranged baled catalyst units (i.e., 103 a-g). Ifdesired, the olefin feed line 104 can be divided into five, six, seven,or a higher number of olefin streams, each of which directs olefin to abaled catalyst unit and wherein there are at least five, six, seven, ora higher number of vertically arranged baled catalyst units.

Preferably, olefin is injected into a lower portion of catalyst beds,thereby leaving one or more (e.g., 1, 2, 3, or 4) catalyst beds of anupper portion of catalyst beds without direct olefin feed. The olefin ismore preferably injected below each catalyst bed of the lower portion ofcatalyst beds. Having catalyst beds above the uppermost olefin feedpoint is particularly advantageous in that these upper catalyst bedsreact the olefin remaining from the catalyst bed above the uppermostsource of olefin feed.

For example, in a particular embodiment, olefin is fed to the firstalkylation catalyst by two to seven split olefin feed lines feeding anequal number of baled catalyst units of a lower portion of a verticalarrangement of three to ten baled catalyst units of the first alkylationcatalyst, wherein the number of baled catalyst units is greater than thenumber of split olefin feed lines, thereby leaving an upper portion ofbaled catalyst units without olefin feed lines.

In another embodiment, olefin is fed to the first alkylation catalyst bythree to five split olefin feed lines feeding an equal number of baledcatalyst units of a lower portion of a vertical arrangement of four toeight baled catalyst units of the first alkylation catalyst, wherein thenumber of baled catalyst units is greater than the number of splitolefin feed lines, thereby leaving an upper portion of baled catalystunits without olefin feed lines.

In the vicinity of where each olefin and aromatic feed line meets thecatalytic distillation unit 100, means are provided for the olefin oraromatic to be distributed onto (or into) the catalyst. The means fordistributing the olefin or aromatic can be any suitable means known inthe art, such as sparging or spraying.

The one or more aromatic compounds in aromatic feed line F-2 arepreferably introduced via a single feed line 105 into the catalyticdistillation unit at any suitable location thereon. In a preferredembodiment, as shown in FIG. 1, the aromatic feed F-2 is introducedbelow the lowermost portion of the first alkylation catalyst, e.g.,below baled catalyst unit 103 a.

The olefin feed in F-1 and the aromatic feed in F-2 can be introducedindependently in a liquid or vapor form. The aromatics are preferablyintroduced into the lowermost portion of the catalytic distillation unit100 below the baled catalyst unit 103 a. The gaseous olefin isdistributed and dissolved in the liquid phase of the aromatic compound.The catalyst is wetted in the liquid phase and the alkylation reactiontakes place in the liquid phase on the catalyst surface.

The olefin feed can contain any suitable concentration of olefin. Forexample, the olefin can be in a low concentration, e.g., 5%, 10%, 15%,or 20% by volume, weight, or mole ratio, or a moderate concentration,e.g., 25%, 35%, 40%, 50%, or 60%. However, the present invention isespecially advantageous for higher concentration of olefin feeds, e.g.,70%, 80%, 90%, 95%, 98%, or higher by volume, weight, or mole ratio.

The source of olefin can be any suitable source. For example, the olefincan be of high purity, such as polymer grade ethylene or propylene.Alternatively, the olefin can be less pure, such as from an offgas froma refinery operation, e.g., from a fluid catalytic cracking (FCC)operation. An offgas source of ethylene can contain, for example,approximately 10% to about 30% by volume of ethylene and approximately50% to 70% methane and hydrogen, as well as minor amounts of other lighthydrocarbon components, such as ethane and propane. Other lightcomponents can include carbon monoxide, carbon dioxide, and/or nitrogen.

The olefin introduced via olefin feed line 104 needs to be capable ofundergoing an alkylation reaction with one or more aromatic compoundsaccording to the process of the invention. For example, the olefin canbe one or more hydrocarbon compounds having two to twenty carbon atomsand at least one double bond. Some examples of suitable olefins includeethylene, propylene, 1-butene, 1,3-butadiene, 2-butene, 1-pentene,1-hexene, 2-hexene, 3-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene,ethylbenzene, styrene, and the divinylbenzenes.

Ethylene and propylene are among the most significant olefins accordingto the present invention since they can be alkylated with benzene tomake at least two commercially important endproducts, ethylbenzene andcumene, respectively.

The one or more aromatic compounds introduced via aromatics feed line105 need to be capable of undergoing an alkylation reaction (i.e.,alkylatable) with one or more olefin compounds according to the processof the invention. Some examples of suitable alkylatable aromaticcompounds useful as feed components in the process described hereininclude benzene, toluene, the xylenes (e.g., o-, m-, and p-xylene),naphthalene, biphenyl, and their derivatives. Benzene is particularlypreferred.

The olefin, once contacted with the aromatic compound in the presence ofthe first alkylation catalyst, reacts with the aromatic compound to formalkylated aromatic compounds, e.g., monoalkylated aromatic compound(e.g., ethylbenzene or cumene) along with a portion of polyalkylatedaromatic compounds. The monoalkylated aromatic compound is typically thedesired product.

Alkylator bottoms effluent 106, which preferably discharges below thelowermost portion of the first alkylation catalyst, includes thesealkylated aromatic products along with some unreacted aromatic, such asunreacted benzene. The alkylated aromatic products from alkylatorbottoms effluent 106 can be separated from each other and from unreactedaromatic according to any suitable processes known in the art, such asby distillation, as further discussed below.

The components discharged above the uppermost portion of the firstalkylation catalyst (e.g., above baled catalyst unit 103 g and intoalkylator overhead stream 108) include, inter alia, unreacted aromatic,unreacted olefin, and typically, an amount of alkylated aromaticcompounds. Alkylated aromatics, if not excluded from the alkylatoroverhead stream 108, will react in the finishing reactor 119 witholefins to produce polyalkylated aromatics. Accordingly, when maximizingselectivity to monoalkylated product is desired, it is preferable thatsuch alkylated aromatic compounds be substantially excluded fromalkylator overhead stream 108 prior to processing the alkylator overheadstream in the finishing reactor 119, by, for example, use of a suitableabsorbent 101 preferably positioned above the uppermost portion of thefirst alkylation catalyst and below where the alkylator overhead streamis discharged.

The absorbent 101 is capable of selectively removing alkylated aromaticcompounds in the presence of unreacted aromatic and olefin compounds,and preferably includes a trayed or packed section capable of providingat least about two to three theoretical stages of removal with the aidof a suitable absorbent. Preferably, the absorbent is a liquid aromaticwhich absorbs the alkylated aromatic compound. The liquid aromatic ispreferably introduced into the upper portion of the absorbent 101 vialine 125 a in order to produce a downward flow of the liquid aromaticagainst the components exiting the uppermost catalyst bed 103 g.

The source of the liquid aromatic absorbent, i.e., liquid aromatics feedline 125 a, is preferably split from a main liquid aromatics feed line125, which is connected to a liquid aromatics feed source F-3. Theliquid aromatics source can be recycled aromatic (e.g., recycledbenzene) recovered from alkylator bottoms effluent 106 by use of anappropriate distillation system, such as shown in FIG. 2, as describedbelow. More preferably, the absorbent is fresh aromatic reactant, e.g.,fresh benzene, since a fresh aromatic source will contain little or noalkylated aromatic compounds, and will thus, more efficiently remove thealkylated aromatics.

In a preferred embodiment, before being fed into the finishing reactor119 via stream line 116, the alkylator overhead stream 108, nowsubstantially removed of alkylated aromatics and containingnon-alkylated aromatics, olefin, and light components, is condensed orsub-cooled (more preferably not sub-cooled) in one or more coolingelements 109 capable of condensing and/or subcooling the overhead stream108. The condensed unreacted olefin/aromatics stream line 111 is thenaccumulated into a finishing reactor feed drum 110, discharged via afeed drum discharge line 113 to one or more finishing reactor feed pumps112, and pumped through a finishing reactor feed pump discharge line 113to a heat exchanger 114 where the condensed alkylator overhead stream ispre-heated by finishing reactor effluent line 120. The preheatedalkylator overhead stream is then fed from heat exchanger 114 via line113 to finishing reactor feed heater 117 for further heating. Liquidaromatics from source F-3 are then combined with the heated finishingreactor feed via split feed line 125 b (preferably containing freshand/or recycled benzene) to control the aromatic to olefin ratio,thereafter forming the finishing reactor inlet stream 116 which containsheated unreacted olefin and aromatics from the alkylator overhead streamas well as additional liquid aromatic from line 125 b, and optionally,some lights.

The finishing reactor effluent stream 120 includes, predominantly,monoalkylated aromatic, polyalkylated aromatic, and unreacted aromaticcompounds, along with gaseous components (i.e., lights), which includessuch gaseous species as methane, ethane, hydrogen, carbon monoxide,carbon dioxide, propane and/or nitrogen. In a preferred embodiment, atleast a portion of the finishing reactor effluent stream 120 is firstcooled (e.g., by cooled stream line 113 in exchanger 114, as shown inFIG. 1), preferably to its bubble point temperature corresponding to thepressure top of the stripper, before being processed in a lightsstripping zone 102. The lights stripping zone includes at least onelights stripper, which can be any suitable lights stripper known in theart, capable of selectively removing gaseous components, as describedabove, from the finishing reactor effluent 120.

Preferably, the lights stripping zone 102 is housed in the uppermostportion of the catalytic distillation unit, and preferably includes oneto five trays, and more preferably, two to four trays. If foundnecessary or desired, the finishing reactor effluent can also beseparately removed of ethane by use of a de-ethanizer, as known in theart. The separated lights in the lights stripping zone 102 can bereleased as overheads through the vent line 128. If desired, the lightscan be condensed and sent to an accumulator. The light stripping zone102 can also stand alone along with suitable bottoms pumps.

The stripped finishing reactor effluent stream 124 is received asbottoms from the lights stripper 102. To further optimize the strippingprocess, a portion of the stripped finishing reactor effluent stream 124is preferably heated in a lights stripper reboiler 126 and recirculatedinto the lights stripper 102 via split line 124 e.

In prior art processes, it is typical for uncooled and unstrippedfinishing reactor effluent to be sent back to the top of the catalyticdistillation unit above the uppermost catalyst bed as reflux to providedownward liquid traffic in the unit. However, unlike what is known inthe prior art, the present invention provides a process wherebyfinishing reactor effluent 124 is stripped of lights in the stripper 102and then cooled, and more preferably sub-cooled, by cooler(s) 123 beforebeing divided amongst the beds (preferably, the lower beds) of the firstalkylation catalyst. Preferably, cooled stream 124 is divided inapproximately equal parts amongst the lower beds of the first alkylationcatalyst to which olefin is being fed, and more preferably, above eachbed of the lower beds of the first alkylation catalyst. The cooledstream 124 is more preferably injected between the catalyst beds,preferably using an internal pipe distributor such as a “ladder type”liquid pipe distributor.

The stream 124 is cooled to a temperature sufficiently low forcondensing at least a portion of vaporous aromatic vapor in thecatalytic distillation unit. Preferably, the stream 124 is cooled to atemperature sufficiently low to re-condense at least a major portion ofthe aromatic compounds vaporized by the heat of reaction in thecatalytic distillation unit, wherein a “major portion” is preferably atleast approximately ninety percent of the aromatic compounds vaporizedin the catalyst bed.

More preferably, the cooled stream 124 is cooled to a temperature thatwould result in condensing the same amount of aromatic that is vaporizedin the catalyst bed below which it is fed. Typically, the stream wouldbe cooled against boiler feed water (BFW) generating low pressure (LP)or medium pressure (MP) steam, which could result in stream temperaturesanywhere from 250° F. to 350° F., depending on steam levels. Heatintegration, in which the stream is exchanged with other process streamsis also possible. In fact, since the temperature at the point in thecatalytic distillation unit at which cooled liquid is fed is typicallyin the range of 365° F. to 482° F., a liquid having a temperature withinor below the foregoing temperature range will result in condensing vaporin the alkylator.

For example, in a preferred embodiment, the stripped and cooledfinishing reactor effluent is introduced into the catalytic distillationunit at a temperature of about 289° F., based on an 18° F. approach tothe LP steam temperature of 271° F. This will typically result in analkylator bottoms temperature (106 stream) of about 430° F. to about436° F.

The cooled finishing reactor effluent stream re-condenses aromatic vapor(e.g., benzene vapor) that was generated by the heat of reactionproduced in the first alkylation catalyst. As a result of thecondensation of aromatic, desired olefin partial pressures are moreeasily maintained and olefin is more evenly distributed throughout thefirst alkylation catalyst, and particularly, at the inlet to at leastthe first and second catalytic reaction zones.

The equalization of olefin partial pressures is particularly importantfor the lower portion of catalyst beds in the first alkylation catalystto which olefin is being fed. The catalyst beds in the upper portion ofthe first alkylation catalyst which do not have a direct feed of olefinare subject to olefin partial pressures which continue to decline in thedirection of the uppermost catalyst bed.

For example, in a preferred embodiment, the variation in olefin partialpressures at the inlets of lower catalyst beds being fed olefin does notexceed about ten percent. More preferably, the variation in olefinpartial pressures at the inlets of lower catalyst beds does not exceedabout five percent, and even more preferably, about one percent. In aparticularly preferred embodiment, the variation in olefin partialpressures is essentially absent, i.e., less than one percent, in thelower portion of catalyst beds (e.g., in olefin feed streams 104 a-104d), and the olefin partial pressures in the lower portion of catalystbeds are essentially equal with a maximum allowable partial pressure ofabout 3.5 bar.

In contrast to prior art processes which require successively greaterolefin feed rates to maintain maximum olefin partial pressure atincreasingly higher catalyst beds in the catalytic distillation column,the process of the present invention can maintain maximum olefin partialpressure with approximately the same olefin feed rates in olefin feedstreams (e.g., 104 a-104 d), which are successively higher in positionin the catalytic distillation column. For example, the olefin feed rateof an olefin feed stream of a second catalytic reaction zone (e.g., 104b), can be approximately the same as the olefin feed rate of an olefinfeed stream of a first catalytic reaction zone (e.g., 104 a), which ispositioned below 104 b of the second catalytic reaction zone. Likewise,the olefin feed rate of olefin feed stream 104 c can be approximatelythe same as the olefin feed rate of olefin feed stream 104 b, which isat a position in the catalystic distillation column below 104 c, and soon, for olefin feeds successively higher up in the column.

Moreover, the olefin feed streams at higher positions in the column canhave olefin feed rates which are lower than the olefin feed rates ofolefin feed streams which are at lower positions in the catalyticdistillation column. For example, the olefin feed rate of 104 a can beone to five percent lower for 104 a as compared to 104 b, 104 c, or 104d.

Since the improvement allows catalyst efficiency to be maintained at ahigh level, olefin can be fed at higher rates to the catalyst withoutsubstantial loss of conversion. Accordingly, the improvement allows forthe use of less catalyst as compared to processes known in the priorart.

Preferably, the stripped and cooled finishing reactor effluent stream124 is fed to the first alkylation catalyst at two or more locations byuse of two or more split feed lines from stream 124. More preferably,stream 124 is split into two to ten and more preferably four to eightsplit feed lines which feed into a vertical arrangement of two to ten,and more preferably four to eight baled catalyst units of the firstalkylation catalyst. Each split stream of cooled finishing reactoreffluent is directed to (and more preferably above) at least one baledcatalyst unit, and the number of split feed lines and number of baledcatalyst units are independent of each other, provided there are atleast as many baled catalyst units as there are split feed lines ofcooled finishing reactor effluent.

In a preferred embodiment, the cooled finishing reactor effluent streamis injected via separate streams to only those catalyst beds in thelower portion of the first alkylation catalyst to which olefin feed isbeing injected. For example, as shown in FIG. 1, cooled finishingreactor effluent is sent to the first alkylation catalyst via stream124, which is split into four streams 124 a-124 d, each of which feedscooled finishing reactor effluent to each of four baled catalyst units(i.e., 103 a-d) in a lower portion of the catalyst beds to which olefinfeed is being injected, out of a total of seven vertically arrangedbaled catalyst units (i.e., 103 a-g) in the catalytic distillation unit100. If desired, the cooled finishing reactor effluent 124 can bedivided into five, six, seven, or a higher number of streams, each ofwhich is fed to a baled catalyst unit and wherein there are at leastfive, six, seven, or a higher number of vertically arranged baledcatalyst units.

It may also be preferred in some embodiments to inject the cooled stream124 above the catalyst beds to which no olefin is being fed. In theupper portion of catalyst beds in which no olefin is being fed, there isstill unreacted olefin present in ever decreasing amounts along with anever decreasing reaction rate, as the uppermost catalyst bed isapproached. Nevertheless, condensing of the aromatic in these uppercatalyst beds has the benefit of increasing the partial pressure of theunreacted olefin, and thus, serves to increase reaction rates above whatthey would be if there were no condensation of aromatics in thesecatalyst beds.

Any number of complementary or auxiliary components can be included inthe process described above for the modification, enhancement, oroptimization of the process. For example, in a preferred embodiment, thealkylator bottoms effluent 106 is further processed via a suitabledistillation process to separate one or more of the products in thealkylator bottoms effluent (e.g., monoalkylated or polyalkylatedaromatics) from other components of the alkylator bottoms effluent, aswell as to recover unreacted aromatic (e.g., recycled benzene).

A preferred distillation system is shown in FIG. 2. Referring to FIG. 2,the alkylator bottoms effluent 106 is preferably first fed via pump 107to distillation column 160 of the distillation unit shown. Column 160separates unreacted aromatic from monoalkylaromatic and heaviercomponents. For example, column 160 can separate benzene fromethylbenzene and heavier components. The aromatic is distilled overheadas a vapor and is preferably liquified by being sent via line 161 tocondenser 162. The liquified aromatic can then be held in an accumulator163, if desired. Liquified aromatic from accumulator 163 can then besent via line 164 back to column 160 as a reflux. A portion of thearomatic can be drawn off from line 164 as liquid aromatic feed line 125(as also shown in FIG. 1) and sent back to the alkylator 100 via splitline 125 a either directly or through any preferred intermediary steps.Bottom stream 167 is preferably recirculated back to the column 160through reboiler 168.

A bottom stream 166 from column 160 is preferably sent to distillationcolumn 170 for separation of the monoalkylaromatic component from thepolyalkylaromatics component. The monoalkylaromatic can include, forexample, ethylbenzene or cumene. The polyalkylaromatics can include, forexample, diethylbenzenes, triethylbenzenes, tetraethylbenzenes,di-n-propylbenzenes, ethyl-n-propylbenzenes, ethylisopropylbenzenes,diisopropylbenzenes, and triisopropylbenzenes. Bottom stream 177 ispreferably recirculated back to distillation column 170 through reboiler178.

The overhead monoalkylaromatic vapor stream 171 from column 170 ispreferably liquified in condenser 172 and sent to accumulator 173. Aportion of the overhead is preferably returned to column 170 as refluxvia line 174. Another portion of the overhead 171 is preferablywithdrawn via line 175 as monoalkylated aromatic (e.g., ethylbenzene orcumene) product P.

Bottom stream 176 containing polyalkylated aromatics is preferablyfurther processed by distillation column 180 for separation ofpolyalkylaromatic (e.g., diethyl benzene), as overhead stream 181, fromflux oil (B), as bottom stream 186. Flux oil typically containsdiphenylethane, tetraethylbenzene, and other high boiling components,and can be discarded or used, e.g., as a heat transfer fluid, fuel oilor an absorbent.

The bottom stream 187 is preferably recirculated back to column 180through reboiler 188. A portion of the bottoms from distillation column180 can be withdrawn via line 186 as the flux oil B. The overheadpolyalkylated aromatics vapor stream 181 is preferably liquified incondenser 182 and sent to accumulator 183. A portion of the overhead canbe returned to column 180 via line 184 as a reflux.

In a further embodiment, a transalkylator can be included in theprocess. A transalkylator reacts polyalkylated aromatic product withnon-alkylated aromatic to produce, predominantly, monoalkylated product.For example, a transalkylator can be included in the process to reactdiethylbenzene and benzene to obtain ethylbenzene as the predominantproduct. To accomplish this, the polyalkylated aromatics stream 185 canbe directly fed into a transalkylator, or indirectly fed through, forexample, one or more vent strippers or vent absorbers.

The transalkylator contains a suitable transalkylation catalyst such aszeolite beta, zeolite Y or other suitable zeolite, and is operated undersuitable transalkylation reaction conditions known in the art. Forexample, the transalkylator can be operated in a temperature of from365° F. to about 482° F. (185° C. to about 250° C.), a pressure of fromabout 350 psig to about 600 psig, a space velocity of from about 3.5 to5.0 WHSV, and a molar ratio of phenyl to ethyl of from about 2.0 toabout 5.0, wherein 3.0 is preferred.

In another aspect, the invention is directed to an apparatus forpracticing any of the alkylation processes described above. Theapparatus preferably comprises: a) a catalytic distillation unit havinga first alkylation catalyst, as described above, b) means forselectively and substantially removing any alkylated aromatic compoundsin the alkylator vapor overhead stream to produce a scrubbed alkylatoroverhead stream, c) means for condensing and transferring the scrubbedalkylator overhead stream to a finishing reactor having a secondalkylation catalyst, as described above, the finishing reactor having afinishing reactor outlet for discharging reacted finishing reactoreffluent, d) means for cooling the finishing reactor effluent to atemperature sufficiently low for condensing at least a portion ofvaporous aromatic compounds in the catalytic distillation unit; and e)means for directing cooled finishing reactor effluent into the firstalkylation catalyst.

In a further embodiment, the apparatus further includes means forremoving a substantial portion of any volatile compounds in thefinishing reactor effluent before cooling step (d) to form a strippedand cooled finishing reactor effluent. In another embodiment, the firstalkylation catalyst comprises at least two lower beds, a lowermost bed,and an uppermost bed. In yet another embodiment, means are provided fordirecting the stripped and cooled finishing reactor effluent to above atleast the two lower beds of the first alkylation catalyst.

Thus, whereas there have been described what are presently believed tobe the preferred embodiments of the present invention, those skilled inthe art will realize that other and further embodiments can be madewithout departing from the spirit of the invention, and it is intendedto include all such further modifications and changes as come within thetrue scope of the claims set forth herein.

1. An apparatus for the production of alkylated aromatic compoundscomprising: a) a catalytic distillation unit having a first alkylationcatalyst, an alkylator bottoms outlet below a lowermost portion of thefirst alkylation catalyst for discharging a liquid alkylator bottomseffluent, and an alkylator overhead outlet above an uppermost portion ofthe first alkylation catalyst for discharging an alkylator vaporoverhead stream, wherein said catalytic distillation unit is operable ina combination liquid-vapor phase under alkylation reaction anddistillation conditions; b) means for selectively and substantiallyremoving any alkylated aromatic compounds in the alkylator vaporoverhead stream to produce a scrubbed alkylator overhead stream; c)means for condensing and transferring said scrubbed alkylator overheadstream to a finishing reactor having a second alkylation catalyst and afinishing reactor outlet for discharging reacted finishing reactoreffluent, wherein said finishing reactor is operable in a liquid phaseunder alkylation conditions; d) means for cooling said finishing reactoreffluent to a temperature sufficiently low for condensing at least aportion of vaporous aromatic compounds in the catalytic distillationunit; and e) means for directing cooled finishing reactor effluent intothe catalytic distillation unit to condense at least a portion ofvaporous aromatic compounds in the catalytic distillation unit.
 2. Theapparatus according to claim 1, further comprising means for removing asubstantial portion of any volatile compounds in the finishing reactoreffluent before cooling step (d) to form a stripped and cooled finishingreactor effluent.
 3. The apparatus according to claim 2, wherein saidfirst alkylation catalyst comprises at least two lower beds, a lowermostbed, and an uppermost bed.
 4. The apparatus according to claim 3,wherein means are provided for directing the stripped and cooledfinishing reactor effluent to above at least the two lower beds of thefirst alkylation catalyst.